The invention relates to a method for packaging products, particularly food products, and for sterilizing them in an alternating high-frequency elctromagnetic field. In a previously known method of this type, such as that disclosed in the German laid-open application 24 18 783, the liquid product is placed in a tube made of a synthetic film, then the tube is passed through a microwave field, which heats the product, and finally the tube is divided into envelope-like packages by the inclusion of a transverse seam, and the packages are separated by cutting through the transverse seam. In the known method, a synthetic packaging material is employed which has a low dielectric loss factor, which presents little resistance to the microwaves and permits them to penetrate into the filling. Packages which are produced in this manner, however, have a shorter shelf life, i.e., keeping capacity of durability, as compared with packages made of metal, because the synthetic film used has a higher permeability to gases.